Monochromatic and Bichromatic Reverse Top-k Queries

Nowadays, most applications return to the user a limited set of ranked results based on the individual user's preferences, which are commonly expressed through top-k queries. From the perspective of a manufacturer, it is imperative that her products appear in the highest ranked positions for many different user preferences, otherwise the product is not visible to potential customers. In this paper, we define a novel query type, namely the reverse top-k query, that covers this requirement: “Given a potential product, which are the user preferences that make this product belong to the top-k query result set?.” Reverse top-k queries are essential for manufacturers to assess the impact of their products in the market based on the competition. We formally define reverse top-k queries and introduce two versions of the query, monochromatic and bichromatic. First, we provide a geometric interpretation of the monochromatic reverse top-k query to acquire an intuition of the solution space. Then, we study in detail the case of bichromatic reverse top-k query, and we propose two techniques for query processing, namely an efficient threshold-based algorithm and an algorithm based on materialized reverse top-k views. Our experimental evaluation demonstrates the efficiency of our techniques.